The
"Up All Night" family is growing: An episode set for October will introduce us to Scott's (
Luka Jones) ex-wife.

She'll be played by the very funny
Mary Elizabeth Ellis of
"It's Always Sunny in Philadelphia,"Zap2it has learned. She's scheduled for the Oct. 18 episode.

Season 2 of the NBC comedy will also bring Blythe Danner back as Scott and Reagan's (
Christina Applegate) condescending mother -- and we'll get to go back in time once again to see her at Chris (
Will Arnett) and Reagan's wedding. No date has been set for Danner's appearance.

Ellis has become something of a go-to guest star lately. In addition to "It's Always Sunny," where she's played the waitress on and off over the years, she was also Nick's (Jake Johnson) ex on
"New Girl" last season and played an oddball acquaintance of Penny's (Casey Wilson) on
"Happy Endings."

She also starred on NBC's
"Perfect Couples" and in the web series
"Georgia."